The invention is based on a fuel injection pump for internal combustion engines. In a fuel injection pump known from German Offenlegungsschrift 32 13 724, the pump piston has as its relief conduit an axial blind bore originating at the pump work chamber, from which bore a transverse conduit branches off to two first outlet openings, and a radial conduit also branches off to a second outlet opening. This second outlet opening is offset with respect to the first outlet openings toward the pump drive side and cooperates with a radial bore, which is disposed in the annular slide and by way of which communication with the relief chamber can be established. In the known fuel injection pump the radial bore is disposed such that, at an annular slide position corresponding to the low-load operating range during the pump piston supply stroke, the second outlet opening is in communication with the radial bore, while in the full-load range, the second outlet opening is not positioned to communicate with the radial bore. The annular slide must be fixed in a constant rotational position during this process, by means of a final control element of the fuel injection quantity regulator, in order for the desired association of the radial bore with the second outlet opening to be maintained. This apparatus serves to allow only some of the supply strokes of the pump piston to be effective in the low-load range; accordingly, a plurality of radial bores are provided, distributed around the annular slide, so that only every other pump piston supply stroke, for instance, leads to a pressure buildup in the pump work chamber and hence to the injection of fuel. Correspondingly, only half of the cylinders of the internal combustion engine serve to drive the engine. This provision is meant to lower fuel consumption in the partial-load range.
A fuel injection pump is also known from German Offenlegungsschrift 32 18 275, in which instead of the radial bores in the annular slide provided in the above-described known fuel injection pump, diametrically extending grooves originating at the end face of the annular slide are provided, which together with the face end of the annular slide serving as a first control edge cooperate with only a single outlet opening of the relief conduit. Thus, the grooves have second control edges for controlling the communication between the pump work chamber and the relief chamber prior to the first control edge coming into play. The annular slide here is not only axially displaceable on the pump piston as a function of the adjustment of a fuel injection quantity regulator, but is also rotatable by a torque device. By means of rotation, during the supply stroke of the pump piston, the outlet opening can be made to come into communication with one of the diametrically extending grooves in alternation, upon every supply stroke, or every other supply stroke, of the pump piston, depending on the number of grooves provided. Thus either the number of injections can be reduced by half, for example, similarly to what is known from the prior art described initially above, or the high-pressure supply of the fuel injection pump can be suppressed entirely. Furthermore, by reducing the width of the grooves, it is possible merely to throttle the outflow or "leakage" of fuel during a particular supply stroke, in order to reduce the fuel injection rate in the lower rpm range. This has the effect, as a so-called quiet-idle device, that the engine can be operated during idling, for example, with reduced combustion noise. The throttling grooves are located, in terms of control effectiveness, upstream of the first control edge.
In this known fuel injection pump, problems arise, however, in terms of controlling the quantity of fuel flowing out via the throttle cross sections. In particular, it is problematic to increase the fuel quantity continuously from a transition from the idling range to the partial-load range, to prevent a load jump upon load take-up. In particular, the outflow of the fuel quantity is dependent, in the known apparatus, on the rpm; that is, it decreases with increasing rpm. Problems also arise if the fuel injection pump has an associated injection onset adjusting device, which typically means that the first outlet opening is adjusted relative to the drive shaft rotational position of the fuel injection pump. For operation at a reduced fuel injection rate by means of leaks via the throttle groove, it has the disadvantage of requiring as many throttle grooves as there are pumping strokes executed by the pump piston per revolution.